Arizona CDL General Knowledge key terms

The total ground distance a vehicle travels from the moment a hazard is seen until it comes to a complete stop. It combines perception distance, reaction distance, and braking distance.

The distance traveled while your eyes and brain notice and identify a hazard ahead. At highway speed this alone can cover a long stretch of road before your foot moves.

The distance covered between recognizing a hazard and actually pressing the brake pedal. It depends on alertness and is longer when you are tired, distracted, or impaired.

The distance needed to stop once the brakes are applied. It grows quickly as speed rises and is much longer on wet, icy, or gravel surfaces, or when brakes are out of adjustment.

Loss of stopping power caused by overheated brake drums and linings, common after repeated hard braking on long downgrades. Shifting to a lower gear and using engine braking helps prevent it.

Using a lower gear so the engine's compression slows the vehicle, reducing reliance on the service brakes. It is the preferred method for controlling speed on steep, long downgrades.

A downhill technique of applying the brakes firmly for a short time to reduce speed, then releasing them to cool. Repeated light, continuous pressure is avoided because it overheats the brakes.

The safety margin of empty road kept around your vehicle so you have room to stop or steer away from trouble. It is maintained ahead, behind, and to both sides.

The gap between your vehicle and the one ahead. Large vehicles need at least one second for each ten feet of vehicle length, plus extra time in poor weather or darkness.

The blind spots around a large vehicle where the driver cannot see other cars, and where those cars cannot see the truck's mirrors. They exist on both sides, directly behind, and in front.

A systematic check of the vehicle performed before driving, covering lights, tires, brakes, fluids, coupling devices, and cargo securement. It is required by regulation and helps catch defects before they cause a breakdown or crash.

A check with the engine off and system fully charged, watching the gauges for pressure loss over time with the brakes released and then applied. Excessive loss means the system must be repaired before driving.

Running the engine to confirm the compressor raises tank pressure from a low reading to the governor cut-out within a reasonable time. Slow buildup points to a weak compressor, leaks, or a bad governor.

A buzzer and light that activate when air tank pressure drops below a set level, warning that braking power is fading. If it comes on while driving, stop safely and find the leak.

The pressure at which the air compressor stops pumping because the tanks are full. Knowing the normal range helps you judge whether the air system is building and holding pressure properly.

Parking and emergency brakes held engaged by heavy springs and released by air pressure. If air pressure is lost, they apply automatically, which is why the vehicle cannot be moved until pressure returns.

The linkage that transfers pushrod force from the brake chamber to the brake shoes. Too much pushrod travel means the brakes are out of adjustment and stopping distance increases.

The maximum allowable pushrod stroke before a brake is considered out of adjustment. A vehicle with brakes beyond this limit is unsafe and must be placed out of service.

The thickness of rubber remaining on a tire's tread. Minimum legal depths apply to front and other tires, and worn tread greatly increases the risk of hydroplaning and blowouts.

A loss of traction that happens when tires ride up on a film of water instead of touching the road. It is more likely with worn tires, high speed, and standing water.

The horseshoe-shaped coupling plate on a tractor that locks onto the trailer's kingpin. A proper tug test after coupling confirms the jaws have closed and locked.

The sturdy vertical pin under the front of a trailer that locks into the tractor's fifth wheel. It carries the pulling force between tractor and trailer and must be fully seated in the jaws.

After coupling, pulling gently forward with the trailer brakes set to confirm the fifth wheel jaws are locked and will not release. The tractor should not be able to pull away.

The retractable legs supporting the front of an uncoupled trailer. They must be fully raised before driving, and cranking them while the trailer is loaded can cause serious injury.

A small axle unit with its own fifth wheel and pintle hitch that couples a second trailer behind the first in a double or triple combination. Its air lines and safety chains must be checked carefully.

A hook-and-latch coupling used to connect a dolly or trailer to a towing vehicle. A safety chain or cable must be attached as a backup in case the hook fails.

Backup chains or cables that keep a trailer attached if the primary hitch fails. They must be crossed where required and strong enough to hold the trailer's weight.

Sideways sway that grows toward the rear of a long combination, where the last trailer swings widest. Smooth steering and steady speed help prevent it from building into a rollover.

The tendency of the rear wheels of a long vehicle to follow a tighter path than the front wheels in a turn. Drivers must swing wide and watch mirrors to keep the trailer off curbs and out of adjacent lanes.

The shifting of liquid inside a partly filled tank as the vehicle changes speed or direction. It can push the vehicle forward, sideways, or into a rollover, so smooth control is essential.

Internal walls inside a tank that divide it into compartments to reduce liquid surge. Even with baffles, a partly loaded tank remains less stable than a full or empty one.

The empty space left above the liquid in a tank to allow for expansion as the product warms. Filling beyond the outage level can cause overflow or damage to the tank.

A special endorsement added to a commercial license after a background check and knowledge test, required to haul regulated hazardous materials. It carries added rules for routing, parking, and communication.

A diamond-shaped warning sign placed on the outside of a vehicle to identify the hazard class of the cargo it carries. Placards alert emergency responders and must match the shipment's shipping papers.

The document describing a hazardous shipment, including the proper shipping name, hazard class, quantity, and emergency contact. It must be kept within reach and shown to inspectors or responders on request.

The system of tiedowns, straps, and blocking used to keep cargo from shifting or falling off the vehicle. Loads must be secured against forward, rearward, and sideways movement before driving.

The combined strength rating of all tiedowns holding a load, which must at least equal half the cargo weight. It is calculated from the marked rating of each strap or chain.

Any strap, chain, rope, or web used to anchor cargo to the vehicle. Each tiedown has a working load limit, and the number and strength of tiedowns must suit the load's weight and length.

The swing-out sign on the driver's side that signals traffic to stop while children load or unload. Drivers must know when the arm is used and how to account for children crossing the road.

The area immediately around a school bus where children are most likely to be hit, extending well in front, behind, and to the sides. Drivers must scan it constantly and never move until children are clear.

A marking on the floor of a passenger vehicle showing where standing riders may not go, keeping the aisle and driver area clear. Passengers must stay behind it while the bus is moving.

The designated area where riders board and exit, which the driver must approach slowly and squarely. The driver must not move until all passengers are seated or safely clear of the vehicle.

A check that the parking brake will hold the vehicle when applied, often done during the pre-trip inspection. On air-braked vehicles it also confirms the emergency spring brakes set when pressure drops.

Where your vehicle sits within the lane, chosen to keep clearance from hazards and to stay visible in mirrors. Large vehicles often need to favor one side to avoid low branches or tight turns.

Operating a vehicle while attention is taken by phones, food, navigation, or other tasks. Even a brief glance away at highway speed covers a long distance blind, so attention must stay on the road.